Process for manufacturing mirror devices using semiconductor technology

ABSTRACT

A method for fabricating a mirror array from a silicon on insulator substrate structure. The method includes providing a silicon-on-insulator (SOI) substrate structure, which may have a material thickness of greater than 10 microns overlying an insulating layer. The SOI material thickness is of a single crystal silicon bearing material. The method also patterns the material thickness using a deep reactive ion etching process to pattern a mirror device structure by forming a trench region that extends from a surface of the material thickness to the insulator structure; and patterns the thickness of material to form a recessed region coupled to the trench region to define a torsion bar structure. The recessed region extends from the surface of the material thickness and is less than about 80% of the mirror device thickness. The method forms an opening on a back side of the SOI substrate structure to the insulator structure. The method removes the insulator material to release the mirror device structure and the torsion bar structure.

This application claims benefit of provisional appln. Ser. No.06/270,404, filed Feb. 20, 2001.

BACKGROUND OF THE INVENTION

This invention generally relates to techniques for fabricating anobject. More particularly, the present invention provides a method forfabricating a switch fabric using one or more semiconductor processingtechniques. Merely by way of example, the present invention isimplemented using such method for a fabric in a wide area network forlong haul telecommunications, but it would be recognized that theinvention has a much broader range of applicability. The invention canbe applied to other types of networks including local area networks,enterprise networks, small switch designs (e.g., two by two or greater)and the like.

As a need for additional switching channels increases, it becomes moredesirable to have larger and larger switching devices. Such switchingdevices must often be capable of switching a beam from one optical fiberto one of a plurality of optical fibers, which can include hundreds ofsuch fibers. Integration of such optical fibers and switching a singlebeam from one fiber to another fiber is often a difficult task by way ofa purely optical technique. Accordingly, there have been many attemptsto make commercial devices that require the need to convert opticalsignals from a first source into electric signals for switching suchoptical signals over a communication network. Once the electric signalshave been switched, they are converted back into optical signals fortransmission over the network.

Numerous limitations exist with such conventional electrical switchingtechnique. For example, such electrical switching often requires a lotof complex electronic devices, which make the device difficult to scale.Additionally, such electronic devices become prone to failure, therebyinfluencing reliability of the network. The switch is also slow and isonly as fast as the electrical devices. Accordingly, techniques forswitching optical signals using a purely optical technology have beenproposed. Such technology can use a wave-guide approach for switchingoptical signals. Unfortunately, such technology has been difficult toscale and to build commercial devices. Other companies have also beenattempting to develop technologies for switching high number of signalsin other ways, but have been generally limited.

For example, Petersen forms a two-dimensional mirror structure withrelatively large design dimensions. We understood that the designdimensions of Petersen were much greater than what is required forhigh-density integrated designs of hundreds of devices and greater.Additionally, Petersen has been effective in forming one or more mirrordevices from a substrate fabric. Such devices often cannot be scaled upto form large arrays of such mirror devices. Petersen also haslimitations in that the deflection devices warp with optical coatings.Additionally, such devices had poor frequency response and operationcharacteristics. A way of controlling device thickness and torsion barthickness also posed a problem. These and other limitations aredescribed throughout this specification and more particularly below.

From the above, it is seen that an improved way to fabricate deflectiondevices is highly desirable.

SUMMARY OF THE INVENTION

According to the present invention, a technique including a method forfabricating an object such as a switch fabric is provided. Moreparticularly, the invention provides a method using one or moresemiconductor processing techniques. Merely by way of example, thepresent invention is implemented using such method for a fabric in awide area network for long haul telecommunications, but it would berecognized that the invention has a much broader range of applicability.The invention can be applied to other types of networks including localarea networks, enterprise networks, small switch designs (e.g., two bytwo or greater) and the like.

In a specific embodiment, the invention provides a method forfabricating a mirror array from a silicon on insulator substratestructure. The method includes providing a silicon-on-insulator (SOI)substrate structure, which may have a material thickness of greater than10 microns overlying an insulating layer, although the substratestructure can be made of other materials. The SOI material thickness isof a single crystal silicon bearing material. The method also patternsthe material thickness using a deep reactive ion etching process topattern a mirror device structure by forming a trench region thatextends from a surface of the material thickness to the insulatorstructure; and patterns the thickness of material to form a recessedregion coupled to the trench region to define a torsion bar structure.The recessed region extends from the surface of the material thicknesstoward the insulator structure and has a depth that is more than about20% of the mirror device thickness in a preferred embodiment. The methodforms an opening on a back side of the SOI substrate structure to theinsulator structure. The method removes the insulator material torelease the mirror device structure and the torsion bar structure.

Many benefits are achieved by way of the present invention overconventional techniques. The invention provides an easy and efficientway of manufacturing high density mirror arrays, e.g., 500 sites, 550sites, 1000 sites, 4000 sites, and greater. The present invention alsocan use conventional process technology, which makes it efficient tomake and use it. By way of the silicon on insulator substrate, theinvention provides an etch stop using the insulator layer sandwichedbetween semiconductor layers. In some embodiments, the invention usesepitaxial silicon as a mirror layer, which is high quality singlecrystal silicon. In most embodiments, the present method is efficient.Depending upon the embodiment, one or more of these benefits may beachieved.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is simplified diagram of an optical switching device according toan embodiment of the present invention;

FIG. 2 is a simplified diagram of an optical deflection device accordingto an embodiment of the present invention;

FIGS. 2A, 2B, 2C, and 2D are more detailed diagrams of an opticaldeflection device according to an embodiment of the present invention;

FIGS. 3-12 are simplified diagrams illustrating methods for fabricatingan optical deflection device according to embodiments of the presentinvention; and

FIGS. 13-18 are simplified diagrams illustrating methods for fabricatingan optical deflection device according to alternative embodiments of thepresent invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

According to the present invention, a technique including a method forfabricating an object is provided. More particularly, the inventionprovides a method using one or more semiconductor processing techniquesfor an improved process. Merely by way of example, the present inventionis implemented using such processing techniques for fabrication of aswitch fabric for a wide area network for long haul telecommunications,but it would be recognized that the invention has a much broader rangeof applicability. The invention can be applied to other types ofnetworks including local area networks, enterprise networks, smallerswitch fabrics (e.g., two by two) and the like. Details of the presentmethod are provided throughout the present specification and moreparticularly below.

FIG. 1 is a simplified diagram of an optical switching device 100according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize many othervariations, modifications, and alternatives. As shown, the device 100for switching one of a plurality of optical signals from a plurality ofoptical fibers 101 is provided. The device has an input fiber bundlehousing 103 comprising an outer side 105 and an inner side 106. Theinput fiber bundle housing has a plurality of sites 107 oriented in aspatial manner on the outer side for coupling to a plurality of inputoptical fibers. Each of the input optical fibers is capable oftransmitting an optical signal. Preferably, the signal is transmittedthrough a lens, which is described in more detail below. The apparatusalso has a first mirror array 109 disposed facing the inner side of theinput fiber bundle housing. The first mirror array 109 includes aplurality of mirrors 111. Each of the mirrors 111 corresponds to one 113of the sites on the outer side of the input fiber bundle housing. Asecond mirror array 115 is disposed facing the first mirror array. Thesecond mirror array is also disposed around a periphery 116 of the inputfiber bundle housing. The second mirror array also has a plurality ofmirrors 117, where each of the mirrors is capable of directing at leastone signal from one of the mirrors on the first mirror array. The devicehas an output fiber bundle housing 119 comprising an outer side 121 andan inner side 123. The output fiber bundle housing has a plurality ofsites 125 oriented in a spatial manner on the outer side for coupling toa plurality of output optical fibers. Each of the sites is capable ofreceiving at least one signal from one of the second mirrors.

The housing is made of a suitable material that is sufficiently rigid toprovide a structural support. Additionally, each housing also hassufficient characteristics to house a fiber optic member. Furthermore,the material also has the ability to provide an array of fiber opticsites, which house fiber optic members. The material can include aconductor, an insulator, or a semiconductor, or any combination ofthese, as well as multi-layered structures. The housing is preferablymade of a similar material as the mirror array to cancel out any thermalexpansion/contraction influences. Preferably, the material is silicon,but can also be other materials. Desirable, the material is also easy tomachine and resists environmental influences. The housing also iscapable of coupling to a lens and/or lens array, which will be describedin more detail below.

Although the above has been described in terms of where the outputarrays are split into a plurality of smaller arrays, the input arrayscan also be split into a plurality of smaller arrays. Here, the outputarray would be a single piece larger array. Alternatively, each of thearrays can be split into a plurality of smaller sections or arrays. Eachof these arrays can be of a similar size or a different size, dependingupon the embodiment. The arrays can also be in a variety of shapes suchas annular, trapezoidal, a combination of these, and others. These andother configurations would be recognized by one of ordinary skill in theart, where there can be many variations, modifications, andalternatives.

FIG. 2 is a simplified diagram of an optical deflection device 200according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize many othervariations, modifications, and alternatives. Like reference numerals areused in this FIG. as some of the others, but are not intended to belimiting. As shown, the mirror array 210 couples to substrate 201, whichwas previously detached from the mirror array. The mirror array can beone of the above, as well as others, which are driven by electrodedevices. The mirror array and substrate couple to each other throughbonding layer 203. The substrate is often a silicon substrate, which canbe made using a semiconductor fabrication process or processes. Thesilicon substrate can include a variety of electrical circuits fordriving electrodes 206, which move each one of the mirrors 202 on themirror array.

As shown, the silicon substrate has a plurality of electrode groups 206an upper surface portion of the substrate. A dielectric layer underliesthe electrode groups. Each of the electrodes couples to lines, whichcouple to drive circuitry. The dielectric layer can be any suitablematerial such as silicon dioxide, aluminum dioxide, silicon nitride,doped silicon glass, spin-on-glass, and the like. The dielectric layercan be a single layer or multiple layers. The electrodes groups are madeof a suitable conductive material, such as aluminum, copper, aluminumalloys, and the like. The material can also be titanium, tungsten, orother barrier type material. The electrodes can also be any combinationof these, as well as others. In some embodiments, a dielectric layer orinsulating layer can be formed overlying the electrodes. The dielectriclayer can be used to protect the electrodes. The dielectric layer can becan be any suitable material such as silicon dioxide, silicon nitride,doped silicon glass, spin-on-glass, and the like. The dielectric layercan be a single layer or multiple layers. The dielectric layer, however,is thin enough to allow the electrodes to influence movement of themirrors on the array.

The substrate includes at least first and second metal layers. A thirdmetal layer can also be included. The second metal layer can be used forthe electrodes 206, as noted above. The first metal layer can be usedfor integrated circuit elements including drive circuitry, senseelectrodes for the mirror, which are able to pick up the very lowcapacitance values without suffering the noise from the interconnects.The substrate can be made using technology of NMOS, CMOS, bipolar, orany combination of these. In an embodiment using CMOS circuitry, thesubstrates includes sense and drive electrodes, multiplexing circuitry(MUX) to multiplex signals from interconnects from the mirror electrodesto reduce the number of connections to the outside world, e.g., wirebonds. The substrate also has drive hold circuitry (and associatedcontrol circuitry) to reduce the overhead necessary to maintain mirrorposition.

In a specific embodiment, the bonding layer can be any suitable materialor materials to connect the mirror array to the substrate. The bondinglayer can be a plurality of bumps 204. In one embodiment, the pluralityof bumps can be made using an IBM C4 process from flip chip technology,i.e., IBM C4 process—Controlled Collapse Chip Connection (i.e.,Flip-Chip Attach (FCA), whereby the chip to be bonded is pre-treatedwith a solder “bump” on each of the bond pads and flipped over andaligned with the underlying substrate for re-flow). This allows forhigh-density (100s to 1000s of interconnects) in a relatively smallarea. The integrated array and substrate are packaged in a carrier.Alternatively, the bonding layer can be made using a deposition process,a screen printing process, an ink jet printing process, aphotolithography process, a eutectic bonding layer, a plated bondinglayer, any combination of these and the like. In a specific embodiment,the carrier can be made of a ceramic material. Alternatively, it couldbe a plastic material. Bonding wires connect each bonding pad 501 to theinterconnect. As shown, the bonding pads are formed on the substratealong a periphery of the mirror array. In a specific embodiment, thebonding pads are provided on the same metal layer as the electrodes.Alternatively, the bonding pads can also be provided on a differentmetal layer. Of course, the specific configuration can depend highlyupon the embodiment. Details of the present device according to thepresent invention are provided below.

FIG. 2A is a simplified top view diagram of a switching device 250according to an embodiment of the present invention. This diagram ismerely an example that should not unduly limit the scope of the presentinvention as defined by the claims. One of ordinary skill in the artwould recognize many other variations, alternatives, and modifications.As shown, the switching device 250 includes a variety of features suchas a deflection device 251. The deflection device 251 is operablycoupled in a first direction to a support structure 254 through aplurality of torsion bars 253. The deflection device is also operablycoupled in a second direction through torsion bars 253 coupled tosupport structure and through a plurality of torsion bars 257 to supportmember 259. The first direction is perpendicular to the seconddirection. As shown, the two pairs of torsion bars provide movement ofthe deflection device in a three dimensional manner. Such dimensionsinclude movement of the deflection device about each of the directionsincluding the first direction and the second direction. The top viewdiagram of the device also illustrates the three reference points. Thefirst reference point is defined by a reference numeral 261. The secondreference point is defined by reference numeral 263. The third referencepoint is defined by reference numeral 265. Details of the device usingcross-sectional view diagrams are provided below.

FIG. 2B is a simplified cross sectional view of the deflection deviceabout reference numeral 261, as previously noted. This diagram is merelyan example that should not unduly limit the scope of the presentinvention as defined by the claims. One of ordinary skill in the artwould recognize many other variations, alternatives, and modifications.As shown, the cross sectional view diagram of the deflection deviceincludes the deflection device to 251. The cross sectional view diagramand also includes a torsion bar 271. A gap or spacing is defined betweenthe torsion bar 271 and the deflection device 251.

FIG. 2C is a simplified cross sectional view diagram of the deflectiondevice about reference numeral 263, as previously noted. This diagram ismerely an example that should not unduly limit the scope of the presentinvention as defined by the claims. One of ordinary skill in the artwould recognize many other variations, alternatives, and modifications.As shown, the cross sectional view diagram of the region defined byreference numeral 263 shows a gap 274 or spacing the define betweensupport structure 254 and support structure 259. The support structure254 is operably coupled to support structure 259 by way of torsion bars257, described above. Each of the support structures is defined on adevice layer that overlies an insulating layer defined on a handlesubstrate.

FIG. 2D is a simplified cross sectional view diagram of a deflection ofdevice about reference numeral 265. This diagram is merely an examplethat should not unduly limit the scope of the present invention asdefined by the claims. One of ordinary skill in the art would recognizemany other variations, and alternatives, and modifications. As shown,the cross sectional view diagram of the region defined by referencenumeral 265 shows a torsion bar 254 position and between supportstructure 259. A gap or spacing 275 is defined between the torsion bar254 and the support structure 259. Details of a fabrication processaccording to an embodiment of the present invention are describedthroughout the present specification and more particularly below.

A method for fabricating a switching device is shown as follows:

1. Provide silicon on insulator silicon substrate (optionally, thesilicon is epitaxial silicon);

2. Grind and polish backside of substrate to thin substrate;

3. Form silicon dioxide (e.g., 3000 Angstroms) overlying topside andbottom side of substrate to form protective layer;

4. Form contact mask overlying top side of protective layer to definecontacts;

5. Etch (e.g., wet dip) to form openings for contacts through protectivelayer;

6. Remove contact mask;

7. Deposit conductive layer (e.g., aluminum) for contacts overlyingsilicon through exposed portions of the protective layer;

8. Pattern conductive layer to form contacts on conductive layer;

9. Form first mask layer on silicon dioxide to define mirror structure;

10. Define mirror structure on silicon dioxide to expose substrateportions;

11. Strip first mask layer;

12. Form oversized mask (second mask layer) relative to exposedsubstrate portions;

13. Etch exposed substrate portions to define regions that will becompletely removed;

14. Selectively remove exposed silicon dioxide;

15. Perform torsion bar etch to continue etching the exposed substrateportions to define mirror to the insulator and define torsion bar, whichis relatively thinner than the mirror;

16. Strip oversized mask;

17. Pattern backside of substrates to define backside of mirror;

18. Etch backside of substrate with pattern up to insulator, which actsas an etch stop layer;

19. Perform selective etch (e.g., deep RIE, wet etch) on insulator ofthe patterned backside to release mirror from the insulator;

20. Form coating on surfaces of mirror (preferably, the coatings coversubstantially all exposed surfaces of the mirror); and

21. Perform other steps as desirable.

The above steps provide an improved way of forming mirror arraystructures coupled to torsion bars. The steps provide a method that doesnot require a difficult to form masking layer. Rather, the method reliesupon at least a combination of oversized mask and related mask to form atorsion bar structure that is much thinner than the thickness of themirror structure. The thinner torsion bar structure can be driven at amuch lower voltage and provides easy operation using conventional drivecircuitry. In an alternative embodiment, the steps provide a method thatcan be easy to perform using conventional semiconductor technology. Thetechnology can be used to form highly integrated mirror arraystructures, where the structures can have a minimum design dimension ofmicrons and less. These and other benefits and details of the presentmethod are provided throughout the present specification and moreparticularly by way of the Figs. below.

FIGS. 3-12 are simplified diagrams illustrating methods for fabricatingan optical deflection device according to embodiments of the presentinvention. These diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.As shown, the method begins by providing a semiconductor substrate 300,which is a silicon bearing material 305 overlying an insulating material303, which overlies a silicon bearing material. Silicon bearing material305 is often single crystal silicon, which may have an overlying layerof epitaxial silicon or epitaxial quality silicon. The substrate can bemade using a silicon layer of about 10-20 microns overlying on insulator(e.g., 3,000 to 10,000 Angstroms), which is formed on the siliconsubstrate (e.g., 525 to 650 microns), but can be made using otherdimensions as well. The surface of the substrate has a uniformity thatis better than one percent or better than 0.5 percent. In a specificembodiment, the substrate is thinned from the backside. Here, thesubstrate is subjected to a grinding and polishing process from thebackside to thin the substrate to about 200 microns, for example, butcan be at other dimensions, as well.

Overlying the silicon layer is an insulating layer 307. The insulatinglayer is often formed using silicon dioxide. The silicon dioxide can bemade using a suitable process such as thermal oxidation, wet oxidation,any combination of these and the like. In a specific embodiment, themethod forms silicon dioxide overlying topside and bottom sides ofsubstrate to form a protective layer, which can be defined as a mask.The protective layer of silicon dioxide can be about 3000 Angstroms, butis not limited. Further details of the process are provided below.

In a specific embodiment, the method forms contacts for electricalconnections to the substrate. These contacts are used to drive and/orsense signals to and from the mirror device. The method for formingcontacts uses conventional masking and etching processes. Here, acontact mask is formed overlying the top side of protective layer todefine contacts openings. The substrate is etched to form openings forcontacts through protective layer. In a specific embodiment, the methoduses a selective etching process such as wet etching using ahydrofluoric acid bearing solution or dry plasma etching. Next, thecontact mask is removed, which exposes contact regions on the substrate.The method deposits a conductive layer (e.g., aluminum) for contactsoverlying exposed regions of silicon through exposed portions of theprotective layer. The conductive layer is patterned to form contacts. Acontact structure is shown in FIG. 4, for example. As shown, thesubstrate includes contact regions 401 in the substrate and overlyingcontact layer 403. The protective layer, which has openings, stillremains on the top surface of the substrate.

In a specific embodiment, the method then patterns the silicon layeroverlying the insulator to define mirror devices and torsion bars, aswell as other elements. The method forms a first mask layer 507 onsilicon dioxide to define a mirror structure, as shown in FIG. 5. Themethod uses conventional masking and etching processes to form openings503 in the masking layer overlying the protective layer. The openingsdefine regions for the mirror device and torsion bar. Here, the mirrordevice underlies photomask at reference numeral 507. The method definesa torsion bar by a region 501 occupied under another portion of thephotomask. An etching step is used to expose the silicon material 601,where the protective layer remains to serve as a mask, as shown by thesimplified diagram of FIG. 6. The diagram also shows that thephotoresist has been stripped.

The method then forms an oversized mask (second mask layer) 701 relativeto exposed substrate portions 601. The oversized mask exposes a portion703 of the protective layer, which still serves as a mask. The surfaceof the substrate is etched to form trench region 803 and torsion barregion 801, as shown in FIG. 8. The etching process can use any suitablechemistry for removing the silicon on the substrate. Here, etching canbe performed using a wet etching process and/or dry etching process.Preferably, the etching process uses a fluorine bearing species.

The method then removes 901 the protective layer to exposes the siliconmaterial of the substrate, as shown in FIG. 9. The surface of thesubstrate is etched in a blanket manner across the entire exposedsurface, including trenches, of the substrate. The etching processdefines a step like feature 1003 adjacent to the photomask. The methoddefines region 1001, which will be the torsion bar. The torsion barregion is at a first level. The method also completely removes siliconmaterial all the way down to the insulating material to define each ofthe mirror structures. The etching process defines both the mirrordevice and the torsion bar structure.

Next, the photomask is stripped, as shown by FIG. 11. The strippingprocess exposes the protective layer 1101, which overlies the mirrorsurface. The method then patterns the backside of the substrate todefine the mirror from the backside. An etching step is performed toremove silicon material from the backside of the substrate. An opening2101 is provided on the backside to remove the silicon substratematerial, as shown in FIG. 12. Preferably, the method uses an etchingprocess such as deep reactive ion etching or the like to remove thesubstrate material from the backside. Preferably, the insulatingmaterial acts as an etch stop for the deep reactive ion etching process.Next, the method performs a selective etching process to removeinsulating material 1203, which is still adhering to the backside of themirror device and torsion bars. The selective etching process often usesa wet etching chemical such as a fluorine bearing species but can alsobe a dry etching process, e.g., plasma etching.

The method then coats 1205 the surfaces of the mirror device to formdesirable optical properties. For example, the method can sputter amaterial such as gold, a gold alloy, chrome, a titanium alloy, or thelike onto surfaces of the substrate. In a specific embodiment, themethod includes forming a reflective surface on the backside of themirror device and further includes forming a reflective surface on afront side of the mirror device to balance mechanical stress between thefront side and the backside to reduce a possibility of warp age onsurfaces of the mirror device. Depending upon the embodiment, the methodcan also perform other steps, which are before, after, or in between anyof the steps described above. Alternatively, the method can remove someof the steps above, as well as combine them to make them moreintegrated. Additionally, some of the steps can be expanded. It is alsounderstood that the examples and embodiments described herein are forillustrative purposes only and that various modifications or changes inlight thereof will be suggested to persons skilled in the art and are tobe included within the spirit and purview of this application and scopeof the appended claims.

A method for fabricating a switching device according to an alternativeembodiment is shown as follows:

1. Provide silicon on insulator silicon substrate;

2. Grind and polish backside of substrate to thin substrate;

3. Form silicon dioxide (e.g., 3000 Angstroms) overlying topside andbottom side of substrate to form protective layer;

4. Form contact mask overlying top side of protective layer to definecontacts;

5. Etch (e.g., wet dip) to form openings for contacts through protectivelayer;

6. Remove contact mask;

7. Deposit conductive layer (e.g., aluminum) for contacts overlyingsilicon through exposed portions of the protective layer;

8. Pattern conductive layer to form contacts on conductive layer;

9. Form first mask layer on silicon dioxide to define mirror structure;

10. Define mirror structure on silicon dioxide to expose substrateportions and underlying insulating layer;

11. Strip first mask layer;

12. Form second mask layer relative to exposed substrate portions todefine a thinner region relative to the mirror structure for at leasttorsion bars;

13. Etch exposed substrate portions to define regions for torsion barssuch that the defined regions do not extend all the way to theinsulating layer;

14. Strip second mask layer;

15. Pattern backside of substrates to define backside of mirror;

16. Perform etch (e.g., deep RIE) on patterned backside to releasemirror;

17. Form coating on surfaces of mirror; and

18. Perform other steps as desirable.

The above steps provide an improved way of forming mirror arraystructures coupled to torsion bars. The steps provide a general methodfor fabricating a mirror array for high integration. The steps provide amethod that can be easy to perform using conventional semiconductortechnology. In a specific embodiment, the technology can be used to formhighly integrated mirror array structures, where the structures can havea minimum design dimension of microns and less. These and other benefitsand details of the present method are provided throughout the presentspecification and more particularly by way of the Figs. below.

FIGS. 13-18 are simplified diagrams illustrating methods for fabricatingan optical deflection device according to alternative embodiments of thepresent invention. These diagrams are merely examples, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art would recognize many other variations, modifications, andalternatives. Like reference numerals are used in these Figs. as some ofthe others. Such numerals are not intended to be limiting in any mannerbut are shown for illustrative purposes. As shown, the method begins byproviding a semiconductor substrate 1300, which is a silicon bearingmaterial 305 overlying an insulating material 303, which overlies asilicon bearing material. Silicon bearing material 305 is often singlecrystal silicon, which may have an overlying layer of epitaxial siliconor epitaxial quality silicon. The substrate can be made using a siliconlayer of about 10-20 microns overlying on insulator (e.g., 3,000 to10,000 Angstroms), which is formed on the silicon substrate (e.g., 525to 650 microns), but can be made using other dimensions as well. In aspecific embodiment, the substrate is thinned from the backside. Here,the substrate is subjected to a grinding and polishing process from thebackside to thin the substrate to about 200 microns, for example, butcan be at other dimensions, as well.

In a specific embodiment, overlying the silicon layer is an insulatinglayer (not shown). The insulating layer is often formed using silicondioxide. The silicon dioxide can be made using a suitable process suchas thermal oxidation, wet oxidation, any combination of these and thelike. In a specific embodiment, the method forms silicon dioxideoverlying topside and bottom sides of substrate to form a protectivelayer, which can be defined as a mask. The protective layer of silicondioxide can be about 3000 Angstroms, but is not limited. Further detailsof the process are provided below.

In a specific embodiment, the method forms contacts for electricalconnections to the substrate, as shown in FIG. 14. These contacts areused to drive and/or sense signals to and from the mirror device. Themethod for forming contacts uses conventional masking and etchingprocesses. Here, a contact mask is formed overlying the top side ofprotective layer to define contacts openings. The substrate is etched toform openings for contacts through protective layer. In a specificembodiment, the method uses a selective etching process such as wetetching using a hydrofluoric acid bearing solution or dry plasmaetching. Next, the contact mask is removed, which exposes contactregions on the substrate. The method deposits a conductive layer (e.g.,aluminum) for contacts overlying exposed regions of silicon throughexposed portions of the protective layer. The conductive layer ispatterned to form contacts. As shown, the substrate includes contactregions 401 in the substrate and overlying contact layer 403. Theprotective layer, which has openings, may still remain on the topsurface of the substrate. Overlying the contact layer is insulatinglayer 1401, which is patterned. The insulating layer can be made of asuitable material such as silicon dioxide, doped silicon dioxide,silicon nitride, and the like. The layer can also be multiple layers andother combinations of layers.

In a specific embodiment, the method uses multiple masking and etchingprocesses to define mirror devices and torsion bar structures. Otherelements may also be defined during one or more of these processes. Themethod forms a first mask layer overlying a surface of the substrate todefine a mirror structure, as shown in FIG. 15. The method usesconventional masking and etching processes to form openings 1501 todefine regions for the mirror device and torsion bar. An etching step isused to remove the silicon material to form the openings, which extenddown to the insulating layer 1503. Next, the photomask is stripped.

The method then forms a second mask layer relative to exposed insulatinglayer to define torsion bar structures. The second mask layer exposes aportion 1601 of the substrate to define a recessed region that does notextend all the way down to the insulating layer. Here, an etchingprocess is often used. The etching process can use any suitablechemistry for removing the silicon on the substrate. Here, etching canbe performed using a wet etching process and/or dry etching process.Preferably, the etching process uses a fluorine bearing species. Next,the method strips the photoresist. Alternatively, the first masking andetching step can be performed after the second masking and etching stepto form the structure in FIG. 16. Here, the second masking and etchingsteps form the larger width openings 1601, which do not extend along theentire thickness of the silicon material. The first masking and etchingsteps form a narrower recessed region 1501, which extends to theinsulating layer. The recessed region has a bottom region 1503, which isdefined on or near the insulating layer. One of ordinary skill in theart would recognize other modifications, alternatives, and variations tosuch masking and etching processes.

The method then patterns the backside of the substrate to define themirror from the backside, as shown in FIG. 17. An etching step isperformed to remove silicon material from the backside of the substrate.An opening 1201 is provided on the backside to remove the siliconsubstrate material. Preferably, the method uses an etching process suchas deep reactive ion etching or the like to remove the substratematerial from the backside. Such etching step removes the silicon allthe way to the insulating layer 303, as shown. Next, the method performsa selective etching process to remove insulating material 303, which isstill adhering to the backside of the mirror device and torsion bars.The selective etching process often uses a wet etching chemical such asa fluorine bearing species but can also be a dry etching process, e.g.,plasma etching. The method completely removes 1203 the insulating layerto release the mirror devices and torsion bars from the insulatinglayer, as shown in FIG. 18.

The method then coats the surfaces of the mirror device to formdesirable optical properties. For example, the method can sputter amaterial such as gold, a gold alloy, chrome, a titanium alloy, or thelike onto surfaces of the substrate. In a specific embodiment, themethod includes forming a reflective surface on the backside of themirror device and further includes forming a reflective surface on afront side of the mirror device to balance mechanical stress between thefront side and the backside to reduce a possibility of warp age onsurfaces of the mirror device. Depending upon the embodiment, the methodcan also perform other steps, which are before, after, or in between anyof the steps described above. Alternatively, the method can remove someof the steps above, as well as combine them to make them moreintegrated. Additionally, some of the steps can be expanded. It is alsounderstood that the examples and embodiments described herein are forillustrative purposes only and that various modifications or changes inlight thereof will be suggested to persons skilled in the art and are tobe included within the spirit and purview of this application and scopeof the appended claims.

One of ordinary skill in the art would recognize many other variations,modifications, and alternatives. The above example is merely anillustration, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize many othervariations, modifications, and alternatives. It is also understood thatthe examples and embodiments described herein are for illustrativepurposes only and that various modifications or changes in light thereofwill be suggested to persons skilled in the art and are to be includedwithin the spirit and purview of this application and scope of theappended claims.

What is claimed is:
 1. A method for fabricating a mirror array from asilicon on insulator substrate structure, the method comprising:providing a silicon-on-insulator (SOI) substrate structure, the SOIhaving a material thickness of greater than 10 microns overlying aninsulating layer, the SOI material thickness being of a single crystalsilicon bearing material; patterning the material thickness using a deepreactive ion etching process to pattern a mirror device structure byforming a trench region that extends from a surface of the materialthickness to the insulator structure; patterning the thickness ofmaterial to form a recessed region coupled to the trench region todefine a torsion bar structure, the recessed region extending from thesurface of the material thickness toward the insulator structure and hasa depth greater than about 20% of the mirror device thickness; formingan opening on a back side of the SOI substrate structure to theinsulator structure; and removing the insulator material to release themirror device structure and the torsion bar structure.
 2. The method ofclaim 1 wherein the deep reactive ion etching process using a fluorinebearing species.
 3. The method of claim 1 wherein the deep reactive ionetching process.
 4. The method of claim 1 wherein the removing stepusing a selective etching process, the selective etching process beingselected from wet etching or plasma etching.
 5. The method of claim 1wherein the forming the opening on the back side of the SOI uses a deepreactive ion etching process that forms the opening of at least 200microns and greater from a backside surface of the mirror device to asurface of the backside of the substrate.
 6. The method of claim 1wherein the insulator provides a buried etch stop layer.
 7. The methodof claim 1 wherein the insulator provides an electrical insulationbetween the mirror device and a remaining portion of the substratestructure.
 8. The method of claim 1 further comprising forming areflective surface on a front side of the mirror device.
 9. The methodof claim 1 further comprising forming a reflective surface on thebackside of the mirror device.
 10. The method of claim 1 wherein thereflective surface is selected from titanium, gold, a combination ofgold and titanium, and chrome.
 11. The method of claim 1 furthercomprising forming a reflective surface on the backside of the mirrordevice and further comprising forming a reflective surface on a frontside of the mirror device to balance mechanical stress between the frontside and the backside to reduce a possibility of warp age on surfaces ofthe mirror device.